The invention relates to a driver of a staple hammer, and more particularly to a driver of a staple hammer that is designed to prevent staples from collapsing.
Staples of various dimensions suitable for various applications are available since staple fastening technique have been extensively used in building houses, doing interior finish work, and the like. The incidence of defective hammering due to collapsing staples increases with an increase in dimensions of staples.
Defective hammering is also related to the fact that hammering resistance increases with an increase in staple length. An example of defective hammering is the following situation. If the top surface of a staple is inclined to the left or to the right due to a staple forming inaccuracy or staple loading defect or if the adhesion strength of a staple is not balanced between the left and right sides, a stress applied to bends S.sub.1, S.sub.2 on both sides of a staple S that is hammered by a conventional driver D whose front end surface is flat is distributed unevenly on both of the left and right sides. As a result, a large stress is applied only to one of the bends, causing the distance between both leg portions S.sub.3, S.sub.4 on the left and right sides of the staple S to be narrowed. The leg portions S.sub.3, S.sub.4 of the staple S with the distance therebetween narrowed are hammered to penetrate into an object so as to come closer to each other in a crossing direction. Since the distance between the leg portions S.sub.3, S.sub.4 at the penetrating positions is smaller than the total width of the top surface of the staple S, the upper portion supported by both leg portions S.sub.3, S.sub.4 collapses before the completion of the staple penetration. This collapse causes a hammering defect such as an incomplete penetration of the leg portions into the object to be hammered B as shown in FIG. 5(b). In the case of a large collapse, the leg portions are jammed in the driver passage of the staple hammer, and as a result the operation may, in some cases, be hampered.